There is the official Ren'Py page: https://www.renpy.org/doc/html/index.html
And I have also written this post on different types of visual novel choices: https://gamejolt.com/p/so-on-tap-for-today-i-want-to-go-over-a-few-simple-choice...
There is also the RenPy subreddit where devs discuss the engine: https://www.reddit.com/r/RenPy/